The present invention relates to a silicone rubber composition for fixing roll service. More specifically, the invention relates to a silicone rubber composition for fixing roll service that is easily molded into a fixing roll as used in devices such as electrophotographic copiers, facsimile machines, and laser printers and that yields a fixing roll with an excellent mechanical strength and excellent toner release properties.
Contact thermal fixing is widely used in electrophotographic copiers, facsimile machines, and laser printers. In this process, the toner image, after its electrophotographic formation on a photoreceptor and transfer to copy paper, is fixed by a fixing roll. The fixing rolls used in contact thermal fixing are fabricated by coating a silicone rubber composition on the circumference of a metal shaft and then curing the composition.
Silicone rubber compositions heretofore proposed for fixing roll service are generally exemplified by the following:
(i) the silicone rubber composition for fixing roll service taught in Japanese Patent Application Laid Open [Kokai] Number Sho 57-149354 [149,354/1982], which consists of alkenyl-containing organopolysiloxane with a viscosity of 100 to 100,000 centipoise at 25.degree. C., organohydrogenpolysiloxane with a viscosity of 1 to 5,000 centipoise at 25.degree. C., inorganic filler, alkenyl-free organopolysiloxane with a viscosity of 10 to 5,000 centipoise at 25.degree. C., and platinum catalyst; PA1 (ii) the silicone rubber composition for fixing roll service taught in Japanese Patent Application Laid Open Number Sho 63-186024 [186,024/1988], which consists of organopolysiloxane that contains at least 2 alkenyl groups in each molecule, organopolysiloxane resin that contains at least 2 silicon-bonded hydrogen in each molecule, and platinum catalyst; and PA1 (iii) the silicone rubber composition for fixing roll service taught in Japanese Patent Application Laid Open Number Hei 4-164741 [164,741/1992], which consists of polyorganosiloxane that contains at least 2 vinyl groups in each molecule and has a viscosity at 25.degree. C. of 500 to 500,000 centipoise, organohydrogensiloxane that contains at least 3 silicon-bonded hydrogens in each molecule, inorganic filler, and a platinum compound. PA1 (A) 100 weight parts diorganopolysiloxane mixture consisting essentially of PA1 (B) 5 to 100 weight parts organopolysiloxane resin with the general formula EQU (R.sub.3 SiO.sub.1/2).sub.x (SiO.sub.4/2).sub.1.0 PA1 in which R denotes a monovalent hydrocarbon group and x has a value of 0.6 to 4.0, PA1 (C) organopolysiloxane that contains at least 2 silicon-bonded hydrogen atoms in each molecule, in a quantity that yields 0.6 to 20 moles silicon-bonded hydrogen in component (C) per 1 mole total alkenyl groups in components (A) and (B), and PA1 (D) platinum catalyst in a catalytic quantity.
However, because the silicone rubber compositions for fixing roll service taught in Japanese Patent Application Laid Open Numbers Sho 57-149354, Sho 63-186024, and Hei 4-164741 contain an inorganic filler such as silica micropowder, quartz powder, and so forth, the fixing rolls obtained therefrom suffer from a gradual decline in their toner release properties with increasing copy mileage and it eventually becomes impossible to obtain clear copies. At the same time, silicone rubber compositions for fixing roll service that lack an inorganic filler such as silica micropowder, quartz powder, etc., yield fixing rolls with a low mechanical strength that will not support practical applications.